This invention relates to a method and apparatus for correcting diametrical taper formed on workpiece journal surfaces, which were previously ground in a large scale manufacturing grinding machine. Taper, as known in the art, is a condition in which the diameter of a bearing surface is not constant along the axial length of the surface. This condition occurs when grinding machines used to grind the workpieces are improperly maintained or when the various abrading means used to remove material from the workpiece are inadequately dressed during operation.
The prior art contains various examples of grinding processes and machines that utilize an in-process gauging system for altering or inducing modifications in a grinding process to correct taper. As it is known in the art, in-process gauging is a method of controlling a grinding or finishing operation in a machine wherein engagement of the grinding or abrading means with the workpiece is controlled in real-time by a measurement signal generated from a gauge that is likewise in contact with the workpiece surface. The grinding process can then be varied and different results achieved by modifying various controls within the grinding process in relation to the gauging signals.
Prior to this invention, in-process gauging was used to correct taper existing on a plurality of diameters on a workpiece by altering the grinding angle of the grinding wheel in relation to the workpiece during the grinding process. An example of this method is disclosed in U.S. Reissue Pat. No. 28,082 to Price, reissued Jul. 23, 1974. The Price patent discloses a multiple or wide wheel grinding machine with a means provided to vary the relative grinding angle between the surfaces of a workpiece to be ground and the grinding wheel.
In the grinding machine of the Price patent, a pair of electrical size gauges are disposed alongside the workpiece on separate axially spaced bearing surfaces. These size gauges generate electrical signals as the workpiece is being rotated about its longitudinal axis during the grinding cycle. The two signals are compared directly and a third signal is generated when the difference between the signals exceeds a predetermined value. The third signal actuates a means for deflecting the grinding wheel and varying the angle of the grinding contact point in response to the third signal, correcting the taper previously existing on the part while it is in the overall grinding process.
U.S. Pat. No. 3,271,910 to Aisch discloses a method for correcting the size and angular relation between a workpiece to be ground and the grinding wheel. Again, two size gauges are axially spaced f rom each other on two different bearing surfaces of a workpiece such as a automotive crankshaft. The two gauge signals measure the diameters at the extreme ends of the workpiece. When differences are noted in the measured diameters and an independent master diameter, a servo motor is engaged to displace the tail stock, thereby changing the angle that the grinding wheel contacts the workpiece surfaces being ground. This displacement continues until deviations from the master diameter are compensated for (i.e. until there is no longer differences between the diameters measured and the master diameter).
As energy efficiency and fuel consumption considerations become more and more important to automotive manufacturers, bearing journal surfaces on internal combustion engine components and related machine components will continue to be machined to closer and closer tolerances. Increased bearing loads, higher operating speeds and greater durability requirements in today's internal combustion engine manufacturers also further the need for precision finishing of journal bearing surfaces. Included with the requirement for more precision finishing is the need to reduce diametrical taper existing on bearing surfaces. As disclosed in the prior art patents above, taper correction was generally utilized as part of the ongoing grinding process and not as an independent operation used to generate higher quality parts.
Prior art methods utilized a modification in angular relation between the longitudinal axis of the workpiece being ground and the longitudinal axis of the grinding tool or wheel. Taper conditions were measured by taking individual diameter readings from two different bearing surfaces spaced axially apart. As disclosed in the prior art patents, the gauge points were generally spaced apart as far as possible by placing one gauge point on the bearing surface closest to one end of the workpiece and one gauge point on the bearing surface closest to the opposite end of the workpiece.
The relative positioning of these gauges is useful in determining whether there is a difference in diameter between the two surfaces being gauged but fails to measure any of the bearing surface configurations spaced axially between the two gauged surfaces on the workpiece. As is known in the art, there are numerous variables in the grinding process such as grinding means dress intervals, grinding means dress quality and the overall general maintenance of the grinding machine. Thus, utilizing in-process gauging to determine the diameters of the bearing surfaces at two axially spaced positions does not give an accurate indication of the diametrical taper conditions that may exist on bearing surfaces spaced between the two engaging positions.
In process gauging in combination with microfinishing operations is disclosed in U.S. Pat. No. 5,095,663 to Judge et al. The Judge et al patent discloses a microfinishing device using in process gauging to measure the diameter of an internal bearing system during the microfinishing process. The microfinishing process is terminated once a predetermined diameter is achieved on the part. The Judge et al patent discloses the use of size control shoes which monitor the diameter of the journal surface using stationary probes in conjunction with air gauges.
The Judge et al patent further discloses the use of an abrasive backed tape to remove material upon the journal surface upon rotation of the workpiece. A microfinishing shoe is used for pressing the abrasive coated film against a portion of a circumference of a journal surface. The microfinishing shoe disclosed is configured as a one-piece, solid, construction capable of applying only grinding forces transferred from the scissor type action of the grinding arm the shoe is affixed to.